The bank originally called a pitch to move the account from Faulds in May 2002, and drew up a shortlist of eight agencies. This was whittled down until only St Luke's remained, but the agency was not appointed, and a new list was formed.
By October, the only agencies in the running were Saatchis and Publicis.
Saatchis will work on further establishing the RBS brand in the market, and it is thought its above-the-line creative strategy will focus in some part on the bank's £15 million sponsorship of The Six Nations rugby tournament.
The agency handled the same sponsorship for Lloyds TSB before it lost the account to Rainey Kelly Campbell Roalfe/Y&R last year.
The most recent campaign from RBS by Faulds, which held the account for ten years, aimed to differentiate the brand from the Bank of Scotland.
Delaney Lund Knox Warren & Partners handles the above-the-line account for Bank of Scotland.
The RBS brand director, Ian Stuttard, said: "We are looking for Saatchi & Saatchi to deliver a powerful creative idea in a complex and cluttered market.
"We are confident it will produce advertising with genuine cut-through, which will help promote the brand and the core values it stands for."